FI patent 71908 discloses a ship of the above type and its loading and unloading system, in which the side port is hinged at its lower end to form a ramp which adjoins an intermediate cargo deck which moves in the vertical direction and is divided into sections so that the ramp and the intermediate cargo deck can be aligned horizontally with the quay irrespective of its height, in which case the cargo units can be driven by a loading trailer into the cargo space of the ship to be further transferred to their final places by means of an overhead crane.
In a ship according to FI patent 71908, the cargo space is of the same height over its entire length, being, in the example case presented, of the height of at least three cargo units plus an overhead crane, in which case the height of the cargo space has to be increased by the height of one cargo unit over its entire length even if the size and stability of the ship would allow the use of only a cargo space of unincreased height, i.e. a cargo space having the height of two cargo units. However, also in the case of smaller ships the cargo space has to be made higher than this in the area adjoining the side ports, in order to enable the intermediate cargo deck to be horizontally aligned with the quay regardless of even great variations in the water level. If it is desired to improve the stability of such a ship, and specifically of a smaller ship of less than 8,000 dwt which has not been equipped with an active stabilization system and the cargo space of which is of equal height over its entire length, the upper part of the covered cargo space has to be left empty, in which case the ratio of covered cargo space to exploited cargo space remains disadvantageous. This results in harbor costs high in proportion to the cargo carried in those countries in which the total capacity of a vessel is the decisive factor in the determination of harbor-dues.
If, on the other hand, the cargo space of such a ship is made lower so that the height of the cargo space corresponds, for example, to only two cargo units plus the space required by the crane, such a system is not capable of operating in a situation in which the proportions of the quay height, ship draft, and water level vary greatly. Such situations appear in almost all harbors, and in most shiploading situations. The problem could possibly be solved by using a floating or otherwise adjustable quay, but such a solution would not be economical.